The invention is directed to an electrographic printer device, particularly a printer or copier, having a first printing unit that applies a first toner image onto an intermediate carrier, and having a second printing unit following the first printing unit in a running direction of the intermediate carrier that applies a second toner image onto the intermediate carrier. Each printing unit contains at least one developer unit. The invention is also directed to a method for printing upon employment of the electrographic printer device.
In many applications, it is necessary to emphasize specific print information within black-and-white print information in color. Examples of this are invoices, forms, address tapes, company logos, etc. A printing carrier with a plurality of colors is already standard with the assistance of ink jet printers. Such printers, however, have a low throughput and are limited to small print jobs. Offset printers can be utilized given larger printing volumes. The combination of successively connected printers that respectively produce one color print has the disadvantage of higher apparatus expense and of the complicated control of both the printing operations as well as the transport.
WO 98/27466 of the same assignee discloses a printer device of the type initially cited. The printer device disclosed therein contains two printing units with a respective developer station that apply toner images onto a single photoconductor band. When the photoconductor band runs, a first character generator generates a first latent charge image that is inked with toner by a first developer station, as a result whereof a toner image is produced. Subsequently, a second character generator generates a second latent charge image on the developed, first charge image by superimposition, said second latent charge image being developed by a second developer station. A second toner image is thus superimposed on the first toner image on the photoconductor band. The resulting toner image is then transferred onto a paper web at a transfer printing location. A two-color toner image can be printed with high printing speed at the transfer location in this way. The charge images generated on the photoconductor band by the two printing units must geometrically exactly fit one another. Further, the toner materials employed in the two developer units must adhere to predetermined, strict material limits with respect to the latent images and must be finely matched to one another. The techniques required for this purpose are technically involved and limit a flexible use.
An object of the invention is to specify an electrographic printer device and a method that allow a simultaneous printing with a plurality of toner images, that are simply constructed and flexibly employable.
According to the method and system of the invention for electrographic printing in a printer or copier, a first printing unit applies a first toner image onto an intermediate carrier. With a second printing unit following the first printing unit in a running direction of the intermediate carrier, the second toner image is applied onto the intermediate carrier. The first printing unit has at least a first developer unit and the second printing unit has at least a second developer unit. With the second developer unit of the second printing unit, a toner is applied onto the intermediate carrier upon employment of a coating method that works without contact. The second toner image is inserted on the intermediate carrier in toner-free regions that are not covered by the first toner image.
According to the invention, the second printing unit has a second developer unit that applies toner onto the intermediate carrier, for example a photoconductor drum or a photoconductor band, upon employment of a coating method that works in non-contacting fashion. Given such a method that works without contact, no color entrainment of the toner image produced by the first printing unit occurs since contact with the first toner image is avoided. Such a color entrainment would substantially reduce the printing quality. The second toner image is inserted on the intermediate carrier in toner-free regions that are not covered by the first toner image. As a result thereof, a superimposition of charge images, which would require a high expense on the part of the intermediate carrier and on the part of the generation of the charge image, is not necessary. Accordingly, the electrographic printer device of the invention is simply constructed.
The coating method of the second developer unit is independent of the coating method of the first developer unit, as a result whereof a highly flexible employment is achieved. For example, it is possible to structurally modify existing electrographic printer devices having only a single printing unit such that a second printing unit is additionally installed, this then applying the coating method that works in non-contacting fashion. The invention thus makes it possible to emphasize company logos, signatures or other image parts with a second toner image, whereby the same units as for the first printing unit that produces the principal printing can be employed to a considerable extent.
According to a preferred exemplary embodiment, the transfer printing from the intermediate carrier onto an ultimate carrier and the fixing of the two toner images occurs in common. In this way, the required hardware expense remains low and existing units can be multiply employed.
According to another preferred exemplary embodiment, the second developer unit contains a developer drum that is coated with toner, whereby a developing gap is present between the intermediate carrier and the developer drum, and toner is transferred onto the surface of the intermediate carrier from the developer drum as a result of an electrical force field between developer drum and intermediate carrier. Such a coating method that works without contact is disclosed by WO 98/27472 of the same assignee and is referred to as a xe2x80x9ctoner jumpxe2x80x9d method. In this method, a latent charge image whose charge potential fluctuates dependent on image structures is present on the intermediate carrier. An electrical field arises in the region of the developing gap, this causing the toner particles to jump from the surface layer of the developer drum onto the intermediate carrier and agglomerate thereto. Since the toner particles only overcome the developing gap when a corresponding charge potential is present on the part of the intermediate carrier, the first toner image is not negatively influenced and no toner materials are entrained.
A toner spraying method is preferably employed as a coating method working without contact, whereby a spray stream of toner-air mixture that is sprayed onto the developer drum is produced. Such a toner spraying method is disclosed by WO 98/57233 of the same assignee. This document is hereby incorporated by reference into the disclosure of the present application. Given a toner spraying method, a developer unit contains a toner spraying unit that generates the stream of toner-air mix. The toner particles having a defined toner charge agglomerate on the surface of the developer drum. From this developer drum, toner particles are transferred onto the intermediate carrier via a developer gap dependent on charge image, and the charge image is inked. This toner spraying method thus works in non-contacting fashion and assures that a first toner image that is already potentially present is not harmed and toner material is not entrained.